System and method for stabilizing a posterior fusion over motion segments

ABSTRACT

A system and method for stabilizing adjacent vertebral bodies that have been fused is provided. The system and method involves transversely securing the bony segments of fused vertebral bodies together. In accordance with one exemplary embodiment, translaminar screws may be employed to transfix the facet joints of one or more motion segments. The motion segment may further include the presence of a spinal fusion implant or other internal fixation device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/941,213, filed Nov. 8, 2010, now U.S. Pat. No. 9,078,701, whichclaims benefit of U.S. Provisional No. 61/259,605, filed Nov. 9, 2009,and entitled “SYSTEM AND METHOD FOR STABILIZING A POSTERIOR FUSION OVERMOTION SEGMENTS,” the entire contents of which are herein incorporatedby reference.

FIELD

The present invention relates to orthopedic implants, and moreparticularly, to spinal implants that facilitate fusion of bone segmentsand associated methods. Even more particularly, the invention relates toa system and method for stabilizing vertebral motion segments.

BACKGROUND

The integrity of the spine, including its subcomponents like thevertebral bodies and intervertebral discs that are well known structuralbody parts forming the spine, is key to a patient's health. These partsmay become crushed or damaged as a result of trauma or injury, ordamaged by disease (e.g., by tumor, autoimmune disease) or as a resultof wear over time or degeneration caused by the normal aging process.

In many instances, one or more structural body parts can be repaired orreplaced with a prosthesis or implant. For example, specific to thespine, one method of repair is to remove the vertebra (in whole or inpart) and/or the disc (in whole or in part) and replace it with animplant or prosthesis. In some cases, it is necessary to stabilize aweakened or damaged spinal region by reducing or inhibiting mobility inthe area to avoid further progression of the damage and/or to reduce oralleviate pain caused by the damage or injury. In other cases, it isdesirable to join together the damaged vertebrae and/or induce healingof the vertebrae. Accordingly, an implant or prosthesis may beconfigured to facilitate fusion between two adjacent vertebrae. Theimplant or prosthesis may be placed without attachment means or fastenedin position between adjacent structural body parts (e.g., adjacentvertebral bodies).

Typically, an implant or prosthesis is secured directly to a bonestructure by mechanical or biological means. One manner of spine repairinvolves attaching a fusion implant or prosthesis to adjacent vertebralbodies using a fixation element, such as a screw. Most implants andtheir attachment means are configured to provide an immediate, rigidfixation of the implant to the implantation site. In certain situations,it is desirable to provide additional stabilization after a posteriorfusion over one or more motion segments.

Although the following discussion focuses on spinal implants orprostheses, it will be appreciated that many of the principles mayequally be applied to other structural body parts within a human oranimal body.

SUMMARY

The present disclosure provides a system and method for stabilizingadjacent vertebral bodies that have been fused by transversely securingthe bony segments together. In accordance with one exemplary embodiment,a spinal stabilization system for transfixing a motion segment of aspine is provided. The system may include a pair of translaminar screwsconfigured for insertion into facet joints of the motion segment, eachscrew comprising a shaft and a head region extending from the shaft. Thesystem may also include a pair of captive washers configured for usewith the translaminar screws, each washer comprising first and secondcomplementary shaped plates for capturing the head region of the screwtherebetween, the second plate further including a hole for receivingthe shaft of the screw. The washers may include bone engaging featuresor surface treatments to promote bony ingrowth. In addition, the screwsand washers permit a range of motion of about 25 to about 35 degrees.

In another exemplary embodiment of the present disclosure, a method isprovided for transfixing a motion segment of a spine. The methodinvolves providing a pair of translaminar screws configured forinsertion into facet joints of the motion segment, each screw comprisinga shaft and a head region extending from the shaft, and a pair ofcaptive washers configured for use with the translaminar screws, eachwasher comprising first and second complementary shaped plates forcapturing the head region of the screw therebetween, the second platefurther including a hole for receiving the shaft of the screw. One ofthe pair of translaminar screws is inserted into a facet joint of themotion segment, while the other of the pair of translaminar screws isinserted into a facet joint on the opposite side of the motion segment.The motion segment further includes the presence of anotherstabilization implant.

Additional features of the disclosure will be set forth in part in thedescription which follows or may be learned by practice of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective cutaway view of an exemplary embodimentof a stabilization system of the present invention in situ.

FIG. 2A illustrates a top view of a washer component of thestabilization system of FIG. 1.

FIG. 2B illustrates a perspective side view of an exemplary embodimentof a screw component of the stabilization system of FIG. 1.

FIG. 2C illustrates a cross-sectional view of the screw component ofFIG. 2B.

FIG. 3A illustrates a side view of another exemplary embodiment of ascrew component of the stabilization system of FIG. 1.

FIG. 3B illustrates a cross-sectional view of the screw component ofFIG. 3A.

FIGS. 4A-4F represent steps in an exemplary method of installing thestabilization system of FIG. 1.

FIG. 5 illustrates a perspective cutaway view of the stabilizationsystem of FIG. 1 used in concert with an exemplary spinal fusionimplant.

FIG. 6 illustrates a perspective cutaway view of the stabilizationsystem of FIG. 1 used in concert with another exemplary spinal fusionimplant.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

The present disclosure provides a system and method for stabilizingadjacent vertebral bodies that have been fused by transversely securingthe bony segments together. As shown in FIG. 1, a stabilization system20 may be provided having translaminar screws 40 and washers 60. Thestabilization system 20 may be employed to transfix the facet joints 8of one or more motion segments, such as vertebral bodies 2, 4 andintervertebral disc 6, in short segments. In the embodiment shown inFIG. 1, the stabilization system 20 is not accompanied by a fusionimplant. However, it is understood that the stabilization system 20 ofthe present invention can be used in concert with many types of knownfusion enabling devices or implants in any region of the spine.Accordingly, FIG. 1 is intended to show the relative positioning of thestabilization system 20 isolated in situ, with the screws 40 shownexaggerated in scale for emphasis.

FIGS. 2A-2C show in greater detail the washer 60 and screw 40 ofstabilization system 20. Referring now to FIG. 2A, the washer 60comprises a lower plate 62 and an upper plate 64. Lower plate may have alumen 66 to accommodate the shaft 44 of screw 40. Referring now to FIG.2B, the washer 60 may also include teeth 68 or another equivalent boneengaging feature such as barbs. As shown in FIG. 2C, the shaft 44extends from a head region 42 having an underside 46 that is contouredto seat within upper plate 64. The upper and lower plates 62, 64 ofwasher 60 form a captive washer for head region 42. The complementaryshape of the underside 46 and the upper plate 64 allows for apredetermined range of motion relative to one another. In oneembodiment, the geometry of the complementary shape supports a range ofmotion in the range of about 25 to about 35 degrees.

As further shown, the shaft 44 may be cannulated to accommodatewire-guided insertion. However, it is contemplated that the screw may bea solid body (i.e., solid core) screw as well, as shown in FIGS. 3A and3B. Both cannulated and uncannulated versions of the translaminar screws40 may be used interchangeably. Referring now to FIGS. 3A and 3B, anuncannulated screw 40 similar to the one described above is shown, withthe same features and configured to be used with the same washer 60, buthaving no through-hole for wire insertion. In both instances with thecannulated and uncannulated versions of the screws 40, the major andminor diameters of the screw thread may be selected to balance thelimited space for installing two or more screws transversely, whileproviding sufficient shear strength. In general, it is preferable tohave the smallest possible major/minor diameters for the screws 40 toallow for ease of insertion, especially to accommodate insertion of thesecond screw.

In the illustrations, screw 40 is shown with a continuous thread alongthe length of the shaft 44 in its entirety. In other embodiments, thescrew 40 is threaded only along a portion of the length of shaft 44,such as the portion that interfaces with the facet joint 8. The screw 40may be a self-drilling and/or self-tapping. A large pitch for screw 40may be helpful for certain embodiments. In addition, screw 40 should beconfigured to avoid any lag effect. In one embodiment, the threads maybe of a buttress type.

The lower plate 62 of washer 60 may be surface treated to promote bonyingrowth. For example, the lower plate 62 may be sintered, plasmatreated, or hydroxyapatite (HA) sprayed on all surfaces that interfacewith bone tissue.

In some embodiments, the present system 20 and associated method may beappropriate for patients having dislocations or subluxations from T12-L1to the lumbosacral junction (L5-S1), supplementary internal fixation ofdegenerative spinal segments treated by an interbody fusion, orposterior alar-transverse or intertransverse fusion in degenerativedisease of the spine.

In an exemplary method of inserting the stabilization system 20, aJamshidi needle may be percutaneously placed at the base of the spinousprocess 10 and inserted interlaminarly into the facet joint 8, as shownin FIG. 4A. Placement of the distal end of the Jamshidi needle may beprovided with a unique geometry to fix a starting point and set thetrajectory of the needle. Through the cannula of the Jamshidi needle, aguide pin can be advanced through to the facet joint 8, as shown in FIG.4B.

Next, as shown in FIG. 4C, a drill guide instrument can bepercutaneously placed at the base of the spinous process 10 and advancedintralaminarly into the facet joint 8. The drill guide instrument may beconfigured with a distal end that is toothed to fix the starting pointat the spinous process 10 and to provide a countersink that matchescaptive washer 60, in order to pre-set mating to the spinous process 10.For example, the handle of the instrument may be rotatable to create aprofile on the cortical bone of the spinous process 10 to help seat thewasher 60. After removing the guide instrument, the cannulated screw 40may be placed over the guide wire and secured in place, as shown inFIGS. 4D and 4E. The surgeon may then repeat the steps above on theopposing side to transversely secure the screws 40 of the system 20 ofthe present invention as shown in FIG. 4F. Although two screws areshown, one skilled in the art will understand that any number of screwsmay be employed, such as one or three screws. Additionally, more thanone stabilization system 20 may be used in a patient. For example, theprocess above may be repeated for a motion segment at a different levelof the spine.

FIGS. 5 and 6 represent other applications of the stabilization system20 of the present invention in concert with exemplary stabilizationimplants, or fusion devices 100, 200, to supplement internal fixation.FIG. 5 illustrates an example of the stabilization system 20 used alongwith a spinal fusion device 100 similar to the one described in U.S.patent application Ser. No. 12/941,190, filed Nov. 8, 2010 and entitled“SPINAL IMPLANT CONFIGURED FOR MIDLINE INSERTION,” now U.S. Pat. No.8,870,961, while FIG. 6 illustrates an example of the stabilizationsystem 20 used along with a spinal fusion device 200 similar to the onedescribed in U.S. Pat. application Ser. No. 12/941,193, filed Nov. 8,2010 and entitled “SPINAL IMPLANT CONFIGURED FOR LATERAL INSERTION,” nowU.S. Pat. No. 8,894,708, both of which are herein incorporated in theirentirety by reference. Of course, it is contemplated that thestabilization system 20 may be used with any number of other types ofstabilization implants or other internal fixation systems or devices.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure. Other embodiments of theinvention will be apparent to those skilled in the art fromconsideration of the specification and practice of the disclosureprovided herein.

What is claimed is:
 1. A spinal stabilization system for transfixing amotion segment of a spine comprising: a pair of translaminar screwsconfigured for insertion into facet joints of the motion segment, eachscrew comprising a shaft and a head region extending from the shaft, thehead region having a smooth, arcuate underside; and a pair of captivewashers configured for use with the translaminar screws, each washercomprising a first upper plate and a second complementary shaped lowerplate, each of the plates including a central opening for receiving theshaft of the screw to capture the head region of the screw therein,wherein the first and second plates each have a spherical contour thatcomplements the smooth, arcuate underside head region such that the headregion of the screw can be seated against, and slidingly move withrespect to, the plates.
 2. The system of claim 1, wherein the washerincludes bone engaging features.
 3. The system of claim 2, wherein thebone engaging features include barbs or teeth.
 4. The system of claim 3,wherein the barbs or teeth extend from one of the plates of the washer.5. The system of claim 1, wherein the screws are cannulated.
 6. Thesystem of claim 1, wherein the screws are non-cannulated.
 7. The systemof claim 1, wherein one of the plates includes a surface treatment forthe promotion of bony ingrowth.
 8. The system of claim 1 wherein thescrews are threaded along their entire length.
 9. The system of claim 1,wherein the screws are partially threaded along their entire length. 10.The system of claim 1, wherein the screws are self-drilling.
 11. Thesystem of claim 1, wherein the screws and washers support a range ofmotion of about 25 to about 35 degrees.
 12. The system of claim 1,wherein the first upper plate and second lower plate are configured toallow sliding movement relative to one another.
 13. The system of claim1, wherein the central opening of the first upper plate is larger thanthe central opening of the second lower plate.